Various software constructs have been developed that communicate with network clients, end users, and associated computing systems. These software constructs include software interfaces, software modules, and other elements that can interact with the end users and often produce data that is transferred back to the end users. For example, web services can include various interfaces and processing elements that handle traffic and requests for user traffic and network-based web clients. Web services can include application programming interfaces (APIs) for clients to communicate with underlying core software packages over network-based interfaces. The core software packages can provide various functionality to end users, such as productivity applications, billing services, storage services, computing services, or other functionality. Many times, these interfaces and portions of the core software packages might be considered ‘legacy’ code which has been operating for many users over an extended timeframe. It can be difficult to modify this legacy code for interfaces and other software services and still ensure that existing clients and customers do not experience bugs or degraded behavior after changes are implemented.